- #1
ezskater
- 9
- 0
Hi all,
(this has originally been in the Materials and Chemical Section. I think it does not belong there).
I'd like to add a question heat dissipation from a brake bad. Basically, let's assume a brake pad is pressed against a surface that quickly moves along (can be the bicycle brake pad on the wheel rim or, in the case of an inline skate with a heel brake, a brake pad and the road itself. Let's look at the latter example in the following). Consider a quasi-stationary case: rolling down a long decline with constant slope and speed. So we have to dissipate some constant power (in the order of a few hundred Watts [10% slope - 10m/s speed - 1 m/s vertical speed - 80 kg mass - 800 N weight - about maybe 50% power dissipated into air friction - makes 400 W]).
In a first order approach I would say that the brake pad would not heat up higher than the temperature of the road. Because that road surface moves along quickly, it does not heat up significantly while the pad glides along. The temperature at the interface road/pad is thus constant. This is where the heat is generated. So the road basically acts like an infinite and "zero-resistive" heat sink.
I think experience does not support this approximation. In particular, if you have an inline skate with a heel brake, the heel brake DOES heat up (does it?). How much? What's wrong with the first order approximation? What would be a more realistic model?
Thanks, Hanno
(this has originally been in the Materials and Chemical Section. I think it does not belong there).
I'd like to add a question heat dissipation from a brake bad. Basically, let's assume a brake pad is pressed against a surface that quickly moves along (can be the bicycle brake pad on the wheel rim or, in the case of an inline skate with a heel brake, a brake pad and the road itself. Let's look at the latter example in the following). Consider a quasi-stationary case: rolling down a long decline with constant slope and speed. So we have to dissipate some constant power (in the order of a few hundred Watts [10% slope - 10m/s speed - 1 m/s vertical speed - 80 kg mass - 800 N weight - about maybe 50% power dissipated into air friction - makes 400 W]).
In a first order approach I would say that the brake pad would not heat up higher than the temperature of the road. Because that road surface moves along quickly, it does not heat up significantly while the pad glides along. The temperature at the interface road/pad is thus constant. This is where the heat is generated. So the road basically acts like an infinite and "zero-resistive" heat sink.
I think experience does not support this approximation. In particular, if you have an inline skate with a heel brake, the heel brake DOES heat up (does it?). How much? What's wrong with the first order approximation? What would be a more realistic model?
Thanks, Hanno